The document “SiGe Bipolar Technology for Mixed Digital and Analog RF Applications”, J. Bock et al. IEEE 2000 discloses transistors of the type mentioned in the introduction in which the base layer has an intrinsic section and an extrinsic section, the extrinsic section connecting a base contact to the intrinsic section. In this case, the extrinsic section has a relatively low boron doping. This results in the disadvantage of a high resistance of the base layer and leads to a reduction of the power gain even at relatively low frequencies and thus to an effective slowing down of the transistor. In addition, the higher base lead resistance brings about higher noise.
U.S. Pat. No. 6,028,345 B1 discloses a method for the production of a transistor comprising an extrinsic base doped in low-resistance fashion, in which a glass layer is deposited in highly doped fashion in the region of the extrinsic base, dopant being driven into the extrinsic base from said glass layer in a thermal step. This method has the disadvantage that the deposition of a sufficiently highly doped layer in a CVD process poses problems.